1. Field of Invention
The present invention relates to automotive interior trim articles containing a panel-like structure constructed to be mounted in an automobile vehicle to form a part of the interior thereof, and in particular to automobile interior trim articles such as instrument panels, door panels, and glove compartment doors. The present invention further relates to a process for making the aforementioned automotive interior trim articles.
2. Description of Related Art
Automotive interior trim articles such as instrument panels, door panels, armrests, headrests, floor consoles, knee bolsters, and glove compartment doors conventionally have been constructed by applying a soft decorative covering over a rigid substrate mountable in an automobile vehicular body, with a cellular polyurethane padding interposed between the decorative covering and rigid substrate. A predetermined texture and color is usually provided to the decorative covering in an effort to simulate the appearance and feel of authentic leather.
The preparation of a self-supporting synthetic automotive interior trim article having a cast polymeric covering, such as a poly(vinyl chloride) (xe2x80x9cPVCxe2x80x9d) covering is known in the art and disclosed in, for instance, U.S. Pat. Nos. 4,562,025, 4,621,995, 4,623,503, 4,923,657, and 5,484,273.
In accordance with these disclosures, slush-or rotational-cast PVC is produced by introducing a liquid plastisol or tumbling a dry PVC powder in a metal mold until the material is formed against a moderately heated mold surface in a gelled state. The gelled material is then fused by heating the material to its fusion temperature and thereafter cooling the material to provide the PVC-based covering in a thermoplastic solid state.
However, in the commercial environment it has been found that PVC coverings prepared in accordance with the conventional techniques set forth in these disclosures must include several chemical additives. These chemical additives are required for at least the following reasons: to ensure that the product has a cosmetically consistent appearance that ages uniformly in use; to protect the coverings from degradation due to excessive temperatures that the coverings encounter during manufacture and use; and to bind the ingredients of the covering in a sufficient manner so as to prevent non-uniform surface appearance due to molecular separation of volatile and migratory ingredients during fusion in manufacture and long term exposure at elevated temperatures, which are often experienced in normal use.
While these additives, which can include heat and ultraviolet light stabilizers and plasticizers, serve the above-mentioned benevolent functions, the additives also can deleteriously affect the appearance of the resultant covering. For example, during manufacture in the rotational casting process disclosed in these related art disclosures, it is not unusual for some of these chemical additives to build up and deposit on the tool surface. Such deposits can hinder the casted material from completely filling the interstices of the grained surface of the mold, thereby preventing the exterior surface of the covering from fully transcribing the grained configuration of the mold surface and causing localized gloss patches to appear on the covering surface. Uniform appearance of color and gloss during manufacture is, therefore, difficult to obtain on a consistent basis without frequent mold cleaning. However, the additional time required to periodically clean the mold surface after demolding of a covering is accompanied by a corresponding loss in productivity. Further, frequent cleaning of the mold surface can cause wear on the grained configuration and shorten the tooling life.
A need therefore exists to provide a process for making a panel-like structure containing a decorative covering with a casted layer, such as a PVC layer or thermoplastic polyurethane layer, in which the panel-like structure can be produced in a more efficient and cost effective manner, and in which the resulting panel-like structure has a high quality, uniform leather-like appearance, and improved grain definition and durability.
It is, therefore, an object of the present invention to solve the aforementioned problems associated with the related art as well as the need expressed above. In accordance with the principles of the present invention, this object is attained by providing a process for making a panel-like structure adaptable for mounting to an automobile vehicle to form a part of the interior thereof. The panel-like structure includes an outer layer defining an exterior surface of the structure, at least a portion of which outer layer is exposed to the vehicle interior, and a rigid substrate defining an interior surface of the structure. The substrate is hidden from the vehicle interior when the panel-like structure is mounted in the automobile vehicle.
According to one embodiment of this process, at least the following steps are performed to prepare the panel-like structure. First, a water-dispersed composition comprising at least one light-stable aliphatic thermoplastic polyurethane containing one or more pendent hydroxyl and/or carboxyl functional groups, a desired coloring agent, and a heat-activated reactive crosslinking monomer or agent is applied onto a heated mold surface shaped to define a corresponding configuration of the outer layer. The heat-activated reactive crosslinking monomer is preferably carbodiimide. The light-stable thermoplastic polyurethane and the heat-activated reactive crosslinking monomer are heated, preferably by pre-heating the mold surface, and reacted to crosslink the thermoplastic polyurethane via the reactive crosslinking monomer. Second, the water-dispersed composition is substantially dried while on the mold surface to form the exposed outer layer with an exterior surface, at least a portion of which has the desired touch, color, and configuration of the panel-like structure. Third, a composition comprising at least one of (i) a poly(vinyl chloride) (xe2x80x9cPVCxe2x80x9d) resin material and at least one suitable plasticizer and (ii) a thermoplastic polyurethane resin material having, for example, at least one ethylenically unsaturated bond in its backbone and suitable additives, is cast against an inner surface of the outer layer while on the mold surface to form an inner layer. In the case of plasticized PVC, the plasticized PVC preferably is cast by gelling and fusing in such a manner that the plasticizer of the plasticized PVC is crosslinked with the polyurethane of the outer layer via unreacted functional groups of the heat-activated reactive crosslinking monomer in the outer layer. In the case of thermoplastic polyurethane resin, it is preferably cast by gelling and fusing in such a manner that unreacted functional groups of the heat-activated reactive crosslinking monomer of the outer layer react with ethylenically unsaturated bonds and/or hydroxyl groups of the thermoplastic polyurethane to crosslink the polyurethane of the inner layer with the polyurethane of the outer layer. Consequently, interfacial chemical bonding is obtained between the inner surface of the outer layer and an adjacent surface of the inner layer during the casting and subsequent cooling steps. Fourth, the inner layer with the outer layer interfacially chemically bonded thereto is united with a rigid substrate so that the rigid substrate serves to reinforce the outer layer. Optionally, a soft cellular polyurethane foam layer can be formed intermediate the inner layer and the rigid substrate. Consequently, the panel-like structure retains the touch and color of the exposed portion and the compressing feel provided to the outer layer by the inner layer and the optional soft cellular foam intermediate layer.
Another object of the present invention is the provision of an automotive interior trim article containing a panel-like structure made by the method of the present invention, and in particular the provision of a panel-like structure having an exterior surface which simulates the appearance and feel of authentic leather.
In accordance with the principles of the present invention, this object is achieved by providing an article comprising a panel-like structure adaptable to be mounted in an automobile vehicle to form a part of the interior thereof. The panel-like structure has an exterior surface exposed to the vehicle interior and an interior surface which is hidden from the vehicle interior when the panel-like structure is mounted to the automobile vehicle structure. The panel-like structure comprises a rigid substrate and layered composition structure. The rigid substrate has one surface defining the interior surface of the panel-like structure, and an opposite surface which is united with the layered composite structure. The layered composite structure comprises an outer layer and an inner layer. The outer layer defines at least a portion of the exposed exterior surface of the panel-like structure, and has the desired touch, color, and configuration of the panel-like structure, as well as exhibiting good chemical resistance. The outer layer comprises a substantially dried, light-stable, crosslinked polyurethane formulated from a water-dispersed composition comprising at least one desired coloring agent, at least one light-stable aliphatic thermoplastic polyurethane containing one or more pendent hydroxyl and/or carboxyl functional groups, and a heat-activated reactive crosslinking monomer or agent. The heat-activated reactive crosslinking monomer is preferably carbodiimide. The light-stable aliphatic thermoplastic polyurethane and the heat-activated reactive crosslinking monomer are heated to thereby produce a crosslinking reaction and molded on a heated mold surface shaped to define a corresponding configuration of the outer layer, and then are dried on the mold surface. The inner layer, which is thicker than the outer layer, comprises at least one of (i) a plasticized PVC formulated from a composition comprising PVC resin and at least one plasticizer and (ii) a polyurethane formulated from a thermoplastic polyurethane resin material having, for example, at least one ethylenically unsaturated bond in its backbone and/or pendant hydroxyl groups. In the case of the PVC resin and plasticizer, the heat-activated reactive crosslinking monomer serves to crosslink the plasticized PVC with the light-stable aliphatic polyurethane of the outer layer. In the case of the thermoplastic polyurethane resin material with an ethylenically unsaturated bond, the heat-activated reactive crosslinking monomer reacts with the ethylenically unsaturated bond and/or hydroxyl group(s) of the thermoplastic polyurethane resin material of the inner layer to crosslink the polyurethane of the inner layer with the light-stable aliphatic polyurethane of the outer layer. Consequently, the inner layer has a surface adjacent to and interfacially chemically bonded with an inner surface of the outer layer. The interfacial chemical bonds are formed by timely gelling and fusing the inner layer against the inner surface of the outer layer while the outer layer is retained on the mold surface. The rigid substrate serves to reinforce the outer layer while retaining the touch and color of the exposed portion and the compressing feel provided to the outer layer by the inner layer and an optional interposed soft cellular polyurethane foam.
The composite provided in accordance with this embodiment exhibits excellent chemical, scuff and mar resistance to external influences. Further, appropriate additives can be introduced into one or both layers of the composite to provide the composite with the non-reflective and low gloss surface appearance desired for such panel-like structures. Furthermore, both the inner and outer layers of the composite are characterized by excellent extensibility, such that the composite can withstand indentation and flexure during use without resulting in cracking in the outer layer over a wide temperature range, such as from xe2x88x9230xc2x0 C. to 120xc2x0 C.
The principles of the present invention enunciated above are applicable to all types of panel-like structures, but have particular applicability to instrument panels (also referred to as dashboards) and door panels. Moreover, the principles of the present invention are applicable to various types of vehicles, including passenger cars, trucks, vans, utility vehicles, and others.